How to design a snake game?

Snake game is a very popular game in the gaming industry. While playing snake game age is not any barrier. You can play this game on any platform, but most players are interested to play on mobile. So, here is a question How to design a snake game?

Now let’s see how to design a snake game with following functionalities:

Snake can move in a given direction and when it eats the food, the length of snake increases.
When the snake crosses itself, the game will over.
Food will be generated at a given interval.
When the snake tries to leave the boundary the snake dies.

This question asked on many interviews like Amazon, Microsoft, etc.

Why did this question raise on interview time? because to check Object-Oriented Functionality Skill among candidates to think about classes.

The main classes will be:

Snake
Cell
Board
Game

The class Game represents the body of our program. It stores the information about the snake and the board.

The Cell class represents the one point of display/board and It contains the row no, column no and the information about it i.e. it is empty or there is a food on it or it is a part of snake body.

To represent a cell of display board

// To represent a cell of display board.
public class Cell {

	private final int row, col;
	private CellType cellType;

	public Cell(int row, int col)
	{
		this.row = row;
		this.col = col;
	}

	public CellType getCellType()
	{
		return cellType;
	}

	public void setCellType(CellType cellType)
	{
		this.cellType = cellType;
	}

	public int getRow()
	{
		return row;
	}

	public int getCol()
	{
		return col;
	}
}

Enum for different cell types

public enum CellType {

	EMPTY,
	FOOD,
	SNAKE_NODE;
}

Now, the Snake class, which contains the body and head.
We have used Linked List to store the body because we can add a cell in O(1).
Grow method will be called when it eats the food. Other methods are self-explanatory.

To represent a snake

// To represent a snake
import java.util.LinkedList;

public class Snake {

	private LinkedList<Cell> snakePartList
		= new LinkedList<>();
	private Cell head;

	public Snake(Cell initPos)
	{
		head = initPos;
		snakePartList.add(head);
		head.setCellType(CellType.SNAKE_NODE);
	}

	public void grow() { snakePartList.add(head); }

	public void move(Cell nextCell)
	{
		System.out.println("Snake is moving to "
						+ nextCell.getRow() + " "
						+ nextCell.getCol());
		Cell tail = snakePartList.removeLast();
		tail.setCellType(CellType.EMPTY);

		head = nextCell;
		head.setCellType(CellType.SNAKE_NODE);
		snakePartList.addFirst(head);
	}

	public boolean checkCrash(Cell nextCell)
	{
		System.out.println("Going to check for Crash");
		for (Cell cell : snakePartList) {
			if (cell == nextCell) {
				return true;
			}
		}

		return false;
	}

	public LinkedList<Cell> getSnakePartList()
	{
		return snakePartList;
	}

	public void
	setSnakePartList(LinkedList<Cell> snakePartList)
	{
		this.snakePartList = snakePartList;
	}

	public Cell getHead() { return head; }

	public void setHead(Cell head) { this.head = head; }
}

The Board class represents the display.

It is a matrix of Cells. It has a method generate Food which generates the food at a random position.

public class Board {

	final int ROW_COUNT, COL_COUNT;
	private Cell[][] cells;

	public Board(int rowCount, int columnCount)
	{
		ROW_COUNT = rowCount;
		COL_COUNT = columnCount;

		cells = new Cell[ROW_COUNT][COL_COUNT];
		for (int row = 0; row < ROW_COUNT; row++) {
			for (int column = 0; column < COL_COUNT; column++) {
				cells[row][column] = new Cell(row, column);
			}
		}
	}

	public Cell[][] getCells()
	{
		return cells;
	}

	public void setCells(Cell[][] cells)
	{
		this.cells = cells;
	}

	public void generateFood()
	{
		System.out.println("Going to generate food");
		while(true){
			int row = (int)(Math.random() * ROW_COUNT);
			int column = (int)(Math.random() * COL_COUNT);
			if(cells[row][column].getCellType()!=CellType.SNAKE_NODE)
				break;
		}
		cells[row][column].setCellType(CellType.FOOD);
		System.out.println("Food is generated at: " + row + " " + column);
	}
}

The main class (Game) keeps the instance of Snake and Board. Its method “update” needs to be called at a fixed interval (with the help of user input).

// To represent Snake Game
public class Game {

	public static final int DIRECTION_NONE = 0, DIRECTION_RIGHT = 1,
	DIRECTION_LEFT = -1, DIRECTION_UP = 2, DIRECTION_DOWN = -2;
	private Snake snake;
	private Board board;
	private int direction;
	private boolean gameOver;

	public Game(Snake snake, Board board)
	{
		this.snake = snake;
		this.board = board;
	}

	public Snake getSnake()
	{
		return snake;
	}

	public void setSnake(Snake snake)
	{
		this.snake = snake;
	}

	public Board getBoard()
	{
		return board;
	}

	public void setBoard(Board board)
	{
		this.board = board;
	}

	public boolean isGameOver()
	{
		return gameOver;
	}

	public void setGameOver(boolean gameOver)
	{
		this.gameOver = gameOver;
	}

	public int getDirection()
	{
		return direction;
	}

	public void setDirection(int direction)
	{
		this.direction = direction;
	}

	// We need to update the game at regular intervals,
	// and accept user input from the Keyboard.
	public void update()
	{
		System.out.println("Going to update the game");
		if (!gameOver) {
			if (direction != DIRECTION_NONE) {
				Cell nextCell = getNextCell(snake.getHead());

				if (snake.checkCrash(nextCell)) {
					setDirection(DIRECTION_NONE);
					gameOver = true;
				}
				else {
					snake.move(nextCell);
					if (nextCell.getCellType() == CellType.FOOD) {
						snake.grow();
						board.generateFood();
					}
				}
			}
		}
	}

	private Cell getNextCell(Cell currentPosition)
	{
		System.out.println("Going to find next cell");
		int row = currentPosition.getRow();
		int col = currentPosition.getCol();

		if (direction == DIRECTION_RIGHT) {
			col++;
		}
		else if (direction == DIRECTION_LEFT) {
			col--;
		}
		else if (direction == DIRECTION_UP) {
			row--;
		}
		else if (direction == DIRECTION_DOWN) {
			row++;
		}

		Cell nextCell = board.getCells()[row][col];

		return nextCell;
	}

	public static void main(String[] args)
	{

		System.out.println("Going to start game");

		Cell initPos = new Cell(0, 0);
		Snake initSnake = new Snake(initPos);
		Board board = new Board(10, 10);
		Game newGame = new Game(initSnake, board);
		newGame.gameOver = false;
		newGame.direction = DIRECTION_RIGHT;

		// We need to update the game at regular intervals,
		// and accept user input from the Keyboard.

		// here I have just called the different methods
		// to show the functionality
		for (int i = 0; i < 5; i++) {
			if (i == 2)
				newGame.board.generateFood();
			newGame.update();
			if (i == 3)
				newGame.direction = DIRECTION_RIGHT;
			if (newGame.gameOver == true)
				break;
		}
	}
}

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